I deleted the media cache and the peak files, and also "cleaned" the database (now called "Delete Unused"). That did not help.

The heart of the problem seems to be calculating "Peak Amplitude." When you open the Audio Gain dialog, you see the calculating message at the bottom. This calculation is now taking about 30-50% of the runtime of the clip. If you normalize after the value is calculated, no problem. If you try to normalize before the calculation is done OR cancel, you will effectively lock up for this period of time in any case. I've had to Force Quit repeatedly just to test this.

I don't remember ever waiting significantly to normalize. It now takes so long I simply can't do it. If you set a new gain level instead of normalizing, that works fine. It simply makes the adjustment.

A second normalization option has been added. I fear there is a bug in the implementation of this.